The present invention concerns dental treatment instruments and more particularly vibrational instruments, such as scaling instruments, which comprise instruments vibrating at audible or ultrasonic frequencies.
This type of instrument, depicted in FIG. 1A, is essentially made up of a handpiece 1 comprising a transducer mechanically coupled rigidly to a vibrating instrument called a “tip” 10, the handpiece being connected to a vibration generator (not depicted). Examples of such tips are described in particular in the documents U.S. Pat. No. 6,312,256 and U.S. Pat. No. 4,283,175.
The tip is an interchangeable part that has a great variety of shapes depending on the use for which it is intended (e.g. scaling: elimination of solid deposits, polishing: elimination of biofilms, grinding: cavities or prosthesis preparations).
As illustrated in FIG. 1A, the existing devices comprise a body 11, most often metallic, one end thereof being assembled rigidly to the transducer of the handpiece 1, the other end of the body 11 being extended by a tool holder itself extended by a tool 12 fixed to the body. This tool comprises a working area that can be a sharp edge, a smooth edge or a smooth surface able to be associated with an abrasive suspension, or else a diamond-charged surface. The vibrations produced by the transducer are thus transmitted directly to the working area of the tool.
So as to be able to be used on all faces of the teeth, the tips are often offered in three shapes: straight, left-hand and right-hand. During a tooth-grinding operation, in particular with a view to a peripheral preparation, the practitioner must use at least two different models of tip: a right-hand and a left-hand.
This is because, owing to the limit of opening of the mouth of the patient and the lateral closure of this cavity by the cheeks which is delimited in FIG. 1A by a line O, the tip must be angled and its movement around the tooth to be ground is relatively limited. The double-ended arrow C shown in FIG. 1A depicts the maximum travel over which the practitioner can move the handpiece 1.
Consequently, during an operation concerning the entire periphery of the tooth, such as for example the peripheral grinding of a tooth 20 aiming to prepare the latter for example for the fitting of a prosthesis (e.g. a crown), the practitioner must use at least two tips: an tip adapted to position the working area of the tool on the front part of the tooth and another tip to position the working area on the back part of the tooth.
More precisely, as depicted in FIGS. 1B and 1C, the practitioner uses a first tip 10a comprising an angled body 11a with the working area 13a of the tool oriented towards the inside so as to be able to grind the back part of the tooth 20 with the working area 13a of the tool 12a and a second tip 10b with an angled body 11b making it possible to grind the front part of the tooth with a working area 13b of the tool 12b turned towards the outside.
In order to avoid having to use two tips during peripheral grinding of a tooth, another solution consists of using a single tip with an axisymmetrical working area. Examples of such a tip are depicted in FIGS. 2A and 2B which show two tips 30a and 30b of different dimensions whereof the body 31a, respectively 31b, is extended by a tool holder and a tool 32a, respectively 32b, having an axisymmetrical working area 33a, respectively 33b, comprising a diamond-charged surface over its entire circumference. Thus, it is possible for the practitioner to carry out peripheral grinding of a tooth 40 with one and the same tip.
Although this solution allows peripheral grinding without requiring too great a travel in the angular movement of the axis of the body of the tip, it has however significant drawbacks. This is because, as illustrated in FIGS. 2A and 2B, owing to the axisymmetrical nature of the working area 32a of the tip, and on account of the latter having to have a rotational shape whereof the section reproduces the preparation shape sought, the tool must have a diameter equal to twice the depth of the grinding, that is twice as large as the width of an asymmetrical tool. In this case, either the tip is unusable, or there is a great risk of attacking part of the adjacent teeth 41, 42.
One solution can consist of using a tool 23b of reduced diameter. However, the use of such an tip considerably reduces the depth of grindings that can be carried out without totally eliminating the risks of damaging the teeth 41 and 42.
Moreover, irrespective of the type of tip used, there exist axial vibrations that bring about shocks in the region of the end of the working area. These shocks can lead to a poor surface condition of the worked parts.
Consequently, the use of vibratory tips, whether asymmetrical or axisymmetrical, in particular for peripheral grinding operations, proves relatively difficult and in this field has few advantages compared with the usual rotary instrumentation techniques.